1. Field of the Invention
This invention relates to a method and apparatus for erasing a magnetic recording track. More specifically, the invention concerns the erasure of a magnetic disk or other magnetic recording medium on which still video pictures are magnetically recorded on a track-by-track basis, and more particularly pertains to a method and apparatus for erasing the recorded information one track at a time or over a range of designated tracks.
2. Description of the Prior Art
Electronic still camera systems have recently been developed. These systems combine an imaging device such as a solid state imaging element or image pickup tube with a recorder that employs an inexpensive rotating magnetic recording medium such as a magnetic disk of a comparatively large storage capacity as a recording medium and operate by electronically imaging a subject, recording a still picture of the subject on the rotating magnetic recording medium and reproducing the recorded picture by a separately provided television system or printer. A video magnetic recording system has also been realized in which a still picture recorded on a visible recording medium such as ordinary film or photographic paper is imaged and recorded on the above-described magnetic recording medium.
In an electronic still camera or video magnetic recording system it is sometimes desired to erase a video signal that has been recorded on a track of the magnetic recording medium and re-record the same or another video signal on this track. In many cases this requirement stems mainly from a recording failure not attributable to a flaw in the magnetic recording medium. Examples of such failures when using an electronic still camera include misfocusing or improper release of the camera shutter. In the case of a video magnetic recording system, failures include improper adjustment of the recorded video signal's white balance, color correction and color density correction. There are also occasions where it is desired to edit the pictures recorded on respective tracks.
When selectively erasing only a specific single track or a predetermined range covering a plurality of tracks, technical problems that require consideration include specifying the position of the track to be erased and setting the range to be erased.
A magnetic recording medium such as a magnetic disk tends to expand and contract somewhat with a change in ambient temperature. Since a video signal is recorded on such a medium with a positional precision on the micron order, the position of each track (the position at which a recording actually exists) shifts when the medium itself expands or contracts, even slightly, due to temperature. With the conventional method of erasing a magnetic recording, track position is detected based on the distance from the position of the origin of the magnetic recording medium and, for this reason, difficulty is encountered in positioning a magnetic head correctly on the desired track. In particular, if a track on which a video signal has been recorded in a high-temperature environment is to be erased in a low-temperature environment, erasure of a location other than that at which this video signal has been recorded is likely to occur. This is because the track position is displaced slightly away from the center of the medium due to medium expansion at the time of recording, and later approaches the center of the medium due to medium contraction at the time of erasure.
Erasure must be performed over a width greater than that at which a recording is made even if the center position of a track has been accurately determined. The reason is that a recorded location tends to meander somewhat, and crosstalk can occur if some information is left unerased. The latter is brought about when the remaining information mixes with information read from the neighboring track or with new information, which has been re-recorded on the same track, when this new information is read. Accordingly, to achieve erasure, it is necessary to use a magnetic head of large width or to provide a small magnetic head, referred to as a tunnel erase head, on both sides of an erase head, thus making necessary an erase magnetic head separate from a write (recording) magnetic head.